1. Field of the Invention
This invention pertains generally to magnetic resonance imaging, and more particularly to a time-resolved, non-contrast enhanced, dynamic MRA (4D dMRA) technique that uses dynamic golden angle radial acquisitions and k-space weighted imaging contrast (KWIC) for image reconstruction that can be used in conjunction with parallel imaging techniques.
2. Description of Related Art
The evaluation of the dynamic flow patterns within the vasculature of the body is desirable for a number of clinical indications, such as steno-occlusive disease, arteriovenous malformation (AVM), and aneurysm. At the present time, intra-arterial digital subtraction angiography (DSA) is considered to be the reference standard for detecting and diagnosing these conditions that provides both high temporal and spatial resolution images of cerebral blood circulation and other vasculature. The DSA procedure, however, is invasive and requires the use of ionizing radiation (X-rays) as well as the injection of iodinated contrast media for imaging that has the associated risks of allergic and other adverse reactions.
Recently, contrast-enhanced dynamic MR angiography (CE-dMRA) has received considerable attention due to its ability to provide temporal information in addition to the otherwise “static” high-resolution 3-D contrast-enhanced MRA for a variety of clinical indications. However, the temporal resolution in CE-dMRA is generally on the order of seconds and the method also requires the intravenous injection of a contrast agent. In the standard MRA examination, 10 to 30 ml of a gadolinium-based contrast agent is typically injected at a flow rate of 1 to 3 mls/s. A test bolus technique is used to define the transit time. A data set is usually collected within 10 to 30 seconds of injection during the peak period of arterial enhancement by the presence of contrast.
In addition, it remains challenging to derive quantitative hemodynamic information using either the DSA and/or the CE-dMRA procedures. For example, imaging of some conditions such as arteriovenous malformations (AVM) requires frame rates greater than 1 frame per second and a special resolution greater than 1 mm in order to properly visualize the complex flow patterns and the vascular anatomy. Therefore, the X-ray DSA diagnostic procedure continues to be the clinical standard for diagnosing some conditions in spite of the undesirable use of ionizing radiation and potentially toxic contrast agents.
Non-contrast enhanced methods of magnetic resonance angiography have also been developed in an attempt to avoid the difficulties associated with acquisition timing, scanner limitations, inconsistent technician skill and contrast use with patients that have poor kidney function. However, past attempts to formulate schemes that reduce the time of acquisition and the amount of contrast exposure while increasing spatial resolution are usually at the expense of SNR and image quality.
Accordingly, there is a need for improved detection and diagnosis of cerebrovascular diseases with a magnetic resonance angiography method that has high spatial resolution for depicting the vascular architecture, as well as high temporal resolution for visualizing the dynamic blood flow patterns, while limiting or eliminating exposure to contrast agents or ionizing radiation.
The present invention satisfies this need as well as others and is generally an improvement over the art.